﻿using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace DPMP.ViewModel
{
    #region Enums

    /// <summary>
    /// Describes the action that caused a CollectionChanging event. 
    /// </summary>
    public enum NotifyCollectionChangingAction { Add, Remove, Replace, Move, Reset }

    #endregion

    #region Delegates

    /// <summary>
    /// Occurs before an item is added, removed, changed, moved, or the entire list is refreshed.
    /// </summary>
    /// <typeparam name="T">The type of elements in the collection.</typeparam>
    /// <param name="sender">The object that raised the event.</param>
    /// <param name="e">Information about the event.</param>
    public delegate void CollectionChangingEventHandler<T>(object sender, NotifyCollectionChangingEventArgs<T> e);

    #endregion

    #region Event Args

    public class NotifyCollectionChangingEventArgs<T> : EventArgs
    {
        #region Constructors

        /// <summary>
        /// Constructor with all arguments.
        /// </summary>
        /// <param name="action">The action that caused the event. </param>
        /// <param name="oldItems">The list of items affected by a Replace, Remove, or Move action.</param>
        /// <param name="newItems">The list of new items involved in the change.</param>
        /// <param name="oldStartingIndex">The index at which a Move, Remove, or Replace action is occurring.</param>
        /// <param name="newStartingIndex">The index at which the change is occurring.</param>
        public NotifyCollectionChangingEventArgs(NotifyCollectionChangingAction action, IList<T> oldItems, IList<T> newItems, int oldStartingIndex, int newStartingIndex)
        {
            this.Action = action;
            this.OldItems = oldItems;
            this.NewItems = newItems;
            this.OldStartingIndex = oldStartingIndex;
            this.NewStartingIndex = newStartingIndex;
            this.Cancel = false;
        }

        /// <summary>
        /// Constructor that omits 'starting index' arguments.
        /// </summary>
        /// <param name="action">The action that caused the event. </param>
        /// <param name="oldItems">The list of items affected by a Replace, Remove, or Move action.</param>
        /// <param name="newItems">The list of new items involved in the change.</param>
        public NotifyCollectionChangingEventArgs(NotifyCollectionChangingAction action, IList<T> oldItems, IList<T> newItems)
        {
            this.Action = action;
            this.OldItems = oldItems;
            this.NewItems = newItems;
            this.OldStartingIndex = -1;
            this.NewStartingIndex = -1;
            this.Cancel = false;
        }

        #endregion

        #region Properties

        /// <summary>
        /// Gets the action that caused the event. 
        /// </summary>
        public NotifyCollectionChangingAction Action { get; private set; }

        /// <summary>
        /// Whether to cancel the pending change.
        /// </summary>
        /// <remarks>This property is set by an event subscriber. It enables
        /// the subscriber to cancel the pending change.</remarks>
        public bool Cancel { get; set; }

        /// <summary>
        /// Gets the list of new items involved in the change.
        /// </summary>
        public IList<T> NewItems { get; private set; }

        /// <summary>
        /// Gets the index at which the change is occurring.
        /// </summary>
        public int NewStartingIndex { get; set; }

        /// <summary>
        /// Gets the list of items affected by a Replace, Remove, or Move action.
        /// </summary>
        public IList<T> OldItems { get; private set; }

        /// <summary>
        /// Gets the index at which a Move, Remove, or Replace action is occurring.
        /// </summary>
        public int OldStartingIndex { get; set; }

        #endregion

    }

    #endregion
}
